Recently, along with the spread of computers and networking of information, e-mail used to transmit and receive character information via networks has come into wide use.
Files in various formats can be attached to e-mail in addition to a mail body consisting of character information. By taking advantage of this feature, Internet FAX (hereinafter abbreviated to IFAX) used to transmit and receive images as attached TIFF (Tag Image File Format) files has come into wide use.
An IFAX transmitter converts image data read by a scanner into TIFF and transmits the converted image data to an IFAX receiver. The IFAX receiver reproduces the TIFF image data from the received data and prints the TIFF image data.
Various methods are available to transmit image data. For example, Japanese Patent Application Laid-Open No. 2000-32202 discloses a technique for transmitting multiple pages of image data by dividing them on a page by page basis.
Also available is RFC (Request for comments) 2045 (issued by the Internet Engineering Task Force—IETF). RFC 2045 describes a method for dividing one e-mail data into multiple pieces of e-mail using “message/partial” as MIME Content-Type and combining the multiple pieces of divided e-mail data into one e-mail data.
Furthermore, RFC 2046 stipulates that an SMTP server which receives and transfers messages must add a “Received:” field containing a “timestamp” and “reception information” to the head of the received messages as path information.
If e-mail is transmitted with a large file attached, intermediary mail servers may be heavily loaded, resulting in a delay in mail delivery. If things get worse, the entire mail delivery service will be stopped. Thus, mail servers are often set not to receive e-mail which is larger than a certain size.
Consequently, if a large volume of image data is transmitted via IFAX, intermediary mail servers may cause delivery error due to the large data size. For example, when transmitting e-mail with an attached file from a PC, it is relatively easy to check the data size of the attached file. In the case of IFAX, however, it is difficult to estimate data size when scanning and transmitting images. This may cause delivery errors frequently.
When transmitting a high-resolution image or color image, even a single page of such an image may involve large data size and delivery errors cannot be avoided even with the technique disclosed in Japanese Patent Application Laid-Open No. 2000-32202.
Even if e-mail is transmitted in the message/partial format described in RFC 2045 and RFC 2046 by being divided into blocks of a predetermined size, a problem described below with reference to FIG. 8 arises.
Referring to FIG. 8, outgoing mail data created for transmission of e-mail consists of a mail header 604, mail body 605, and attached TIFF file 606. The mail body 605 does not have to exist.
Upon receiving the outgoing mail data from a transmitter, a mail server adds a “Received:” field 603 to the head of the outgoing mail data according to RFC 2046. When the outgoing mail data is transferred to another mail server, another “Received:” field 602 is added to the head of the outgoing mail data. If this is repeated, “Received:” fields such as 601 and 600 are piled up, ever enlarging the outgoing mail data.
Thus, even if outgoing mail data are transmitted after being divided into blocks of a predetermined size, their size increases as they pass mail servers on the route. Consequently, even if e-mail is transmitted keeping within data size limits set for mail servers, the limits are exceeded in mid-course, resulting in a delivery error of a mail server.